The next biggest properties were Microsoft Sites with 174.4 million and Yahoo sites with 173.5 million. Facebook, meantime, came in at number four with 158.6 million visitors, and, curiously, MySpace jumped 8 positions to rank number 42 with 25.5 million visitors.

Remember: This is strictly visitors, not a measure of how long people spend on these sites.

Yet one standout from the report is Pinterest, the invitation-only site that at the end of least year ranked as a top 10 social site.

Pinterest, a place where people create virtual pinboards from things they find across the Web, saw its number of unique visitors jump 52 percent from January to February, to more than 17.8 million.

Top 10 percentage gainers in February in terms of unique visitors

Other big gainers aren't as surprising. The IRS site, for instance, would naturally get more attention given that it's tax season. And the Super Bowl was a big traffic boon to automakers.

More than 27 million people visited automaker sites in February, a gain of 17 percent versus January. Toyota led the group with 6.4 million visitors (up 20 percent), followed by Honda with 5.1 million (up 42 percent) and General Motors with 4.8 million (up 6 percent). Chrysler, which ran a Super Bowl ad featuring Clint Eastwood's "Halftime in America," posted a 17 percent increase to rank sixth with 2.7 million visitors.